Closure pieces and powder syringes of the presently mentioned kind are known in the art. Dual chamber systems having a proximal and a distal chamber are preferably used as powder syringes. The proximal chamber typically comprises a liquid solvent and is separated from the distal chamber by a central plug, which includes a material that is soluble in the solvent. Said material can be a free-flowing powder. Known closure pieces include a channel that is in communication with the distal chamber, on the one hand, and that can be brought in fluid communication with a cannula or needle of a syringe that is attached to the closure piece, on the other hand. It is possible for powder to enter the area of the closure piece that is provided for the channel and/or into the channel itself. This can cause clumping, meaning the formation of agglomerates of the powder-type material, and the material may no longer be soluble. When this occurs, the channel is blocked such that the dual chamber system is no longer usable. The same problem also exists with a powder syringe that is not configured as a dual chamber system but that includes one closure piece with one channel. Powder agglomerates can form inside the channel in this instance as well, thus blocking the channel.